Exogenous insulin promotes the expression of B-cell translocation gene 1 and 2 in chicken pectoralis

Abstract

B-cell translocation genes (BTG) have been proved to play important roles in carbohydrate metabolism through modifying insulin homeostasis and glucose metabolism. This study, therefore, was conducted to investigate the effects of exogenous insulin on the expression of BTG1 and BTG2 in chickens. Twenty-four-day-old broilers and layers were fasted for 16 h and randomly assigned to insulin treatment group (subcutaneously injected with 5 IU/kg body weight) or control group (received an equivalent volume of phosphate-buffered saline). Blood glucose concentration was measured, and it showed that the blood glucose concentrations in the layers were significantly (P < 0.05) higher than that in the broilers under fasting state. Response to exogenous insulin, the blood glucose concentrations were greatly reduced in both breeds. Of note, the blood glucose concentration restored to 62% of the basal state at 240 min (P < 0.05) after insulin stimulation in layers, whereas it was still in low level until 240 min in broilers (under fast state). Tissue profiling revealed that both BTG1 and BTG2 were abundantly expressed in the skeletal muscles of broilers. A negative correlation was observed between blood glucose and BTG1 (ρ = -0.289, P = 0.031) /BTG2 (ρ = -0.500, P < 0.001) in pectoralis, and BTG1 (ρ = -0.462, P < 0.001) in pancreas. As blood glucose decreased due to exogenous insulin administration (under fast state), the expression of both BTG1 and BTG2 notably upregulated in birds' pectoralis at 120 min and/or 240 min, meanwhile pancreas BTG1 was also upregulated. Re-feeding at 120 min elevated the blood glucose and reduced the expression of BTG genes in pectoralis generally. In addition, the change of BTG1 and BTG2 expression showed distinct difference between layers and broilers at 120 min and 240 min after insulin stimulation in pectoralis, pancreas and heart tissue; even after re-feeding at 120 min, BTG2 expression at 240 min after insulin injection was downregulated in the pectoralis of layers, while it was upregulated in that broilers. Collectively, these results indicated that response to exogenous insulin, chicken blood glucose exhibited breed-specific dynamic change, and meanwhile the expressions of both BTG1 and BTG2 genes in chickens were significantly altered by exogenous insulin in a breed- and tissue-specific manner. BTG1 and BTG2 genes may negatively regulate bird's blood glucose by promoting the glucose uptake corporately in pectoralis, and through regulating the insulin secretion in pancreas (especially BTG1).

Keywords: BTGs; blood glucose; chicken; insulin.

Figure 1

Effect of exogenous insulin on blood glucose concentration. (A) Chickens were in a fasting state. Different letters across time indicate P < 0.05 in the same treatment group. Between the LP and LI group at the same time-point, * indicates P < 0.05, ** P < 0.01. Between the BP and BI groups at the same time points, # indicates P < 0.05, ## P < 0.01. Between the LP and BP groups at the same time points, ▲ indicates P < 0.05, ▲▲ P < 0.01. Between the LI and BI groups at the same time points, & indicates P < 0.05, && P < 0.01. Absence of a letter or symbol or the same letter indicates P > 0.05. (B) Blood glucose concentrations of chickens at 240 min after insulin or PBS injection. “NF”: no feed was provided after 120 min. “WF”: feed was provided after 120 min. * indicates P < 0.05, ** P < 0.01. Different letters indicate P < 0.05 in different treatment groups under NF or WF conditions. Absence of a letter or symbol or the same letter indicates P > 0.05. Abbreviations: BI, insulin-treated broilers; BP, PBS-treated broilers; LI, insulin-treated layers; LP, PBS-treated layers.

Figure 2

BTG1 and BTG2 mRNA levels. Chickens were in a fasting state. (A and C) Relative abundances of BTG1 and BTG2 mRNAs in different tissues in the basal state of broilers. Chickens were slaughtered after fasting for 16 h (n = 4 per breed). (B and D) Levels of BTG1 and BTG2 mRNAs in insulin-sensitive tissues in the basal state. Different letters across tissues indicate P < 0.05 in the same breed. Absence of letter or the same letter indicates P > 0.05.

Figure 3

Expression of BTG1 at different time points after injection of exogenous insulin. Chickens were in a fasting state. Different letters across times indicate P < 0.05 in the same treatment group. * indicates P < 0.05. ** indicates P < 0.01. Absence of letter or * or the same letter indicates P > 0.05. Abbreviations: BI, insulin-treated broilers; BP, PBS-treated broilers; LI, insulin-treated layers; LP, PBS-treated layers.

Figure 4

Expression levels of BTG2 at different time points after injection of exogenous insulin. Chickens were in a fasting state. Different letters across time points indicate P < 0.05 in the same treatment group. * indicates P < 0.05. ** indicates P < 0.01. Absence of letter or * or the same letter indicates P > 0.05. Abbreviations: BI, insulin-treated broilers; BP, PBS-treated broilers; LI, insulin-treated layers; LP, PBS-treated layers.

Figure 5

Effects of feeding chickens (or not) at 240 min after insulin injection on their BTG1 and BTG2 expression. Expression of BTG1 in layers (A) and broilers (B). Expression of BTG2 in layers (C) and broilers (D). Chickens were fed or continued fasting at 120 min after injection with insulin or PBS. “WF + PBS/Insulin”: indicates feed was provided to the chickens and they were treated with PBS or insulin. “NF + PBS/Insulin” indicates that feed was not provided to the chickens and they were treated with PBS or insulin. * indicates P < 0.05. ** indicates P < 0.01. Absence of * indicates P > 0.05.